| Popis: |
The corepressor CtBP (carboxyl-terminal binding protein) is involved in transcriptional pathways important for development, cell cycle regulation, and transformation. We demonstrate that CtBP binding to transcription repressors is stimulated by NAD+ and NADH, with NADH being two to three orders of magnitude more effective. Fluorescence resonance energy transfer studies of CtBP show a > 100-fold higher affinity for NADH than NAD+, in agreement with the tighter interaction observed in the crystal structure of NADH-bound CtBP. Levels of free nuclear nicotinamide adenine dinucleotides, determined using two-photon microscopy, correspond to the concentrations required for half-maximal CtBP binding. Free cellular NAD+ concentration greatly exceeds that of NADH and the redox changes are mainly reflected by NADH levels. Agents increasing NADH levels stimulate CtBP binding to its partners in vivo and potentiate CtBP-mediated repression. These findings suggest that the transcriptional corepressor CtBP may serve as a redox sensor to provide a link between gene expression and metabolism. |
